1. Field of the Invention
The present invention generally relates to a method and apparatus for improving manufacturing line performance and more specifically to a method that includes both the status of the tool and the status of the lot when calculating manufacturing line performance.
2. Description of the Related Art
The major thrust of manufacturing line performance improvements in, for example, the semiconductor fabrication industry, has primarily focused on using overall equipment effectiveness (OEE) to measure and manage tool productivity. These conventional efforts use many tool state data collection systems, some of which use manually input data and others which use signals automatically input from the tool itself.
There is a relationship between cycle time and tool the utilization which is evaluated by comparing the normalized cycle time (X-factor) and the idle-no-WIP (work in progress) machine status. The X-factor is the cycle time divided by raw processing time. The cycle time is the time necessary for a workpiece to wait for the tool and to be processed by the tool and the raw processing time is only the time necessary for the tool to actually perform work on the workpiece. The xe2x80x9ceffective capacityxe2x80x9d of a tool is the maximum throughput possible given the capacity detractors in the production line. The difference between the throughput and the effective capacity is the amount of idle-no-WIP. As throughput is increased toward effective capacity, thus reducing the idle-no-WIP, the cycle time, and hence x-factor, must necessarily increase as additional workpieces are placed before the tool. The cost of lower cycle times is the larger amounts of idle-no-WIP times.
One of the capacity detractors for a production line occurs when operators are not available to load or unload tools precisely when required. This lack of availibility can be due to other tasks which they are required to perform or can be due to such activities such as lunch or break. Therefore, the unavailability of an operator further increases capacity loss which increases the cycle time and X-factor by reducing the amount of idle-no-WIP.
Conventional measurement and tool management systems concentrate on the tool status or on lot status to determine the production line""s effectiveness. Because such conventional systems are based exclusively on optimizing individual productivity classifications (e.g., tool, lot, etc.), the correlation between the operator and the tool element is difficult to measure and optimize. Further, operator activity and/or availability is conventionally measured manually, either through management observation or through operator record keeping (automated or manual). Such manual systems of monitoring operators fall victim to substantial subjective input and estimation inaccuracies.
The invention disclosed below accounts for both tool optimization and operator optimization to more precisely achieve higher production line efficiencies.
It is, therefore, an object of the present invention to provide a computer system, computer program product and a method for evaluating manufacturing line performance that includes determining tool status, determining lot status and combining the tool status and the lot status to produce status codes. The status codes include a running code, a tool down code, a no operator code, and an idle no work-in-process code.
The tool status includes one of the tool down code, the running code and a tool idle code. The lot status includes one of a waiting to be processed code and a being processed code. The no operator code is produced when the tool status is the tool idle code and the lot status is the waiting to be processed code. The idle-no-WIP code is produced when the tool status is in an idle code and there are no lots waiting to be processed. The determining of the tool status and the determining of the lot status are performed automatically by a computerized system.
Another embodiment of the invention is a system for evaluating manufacturing line performance that includes a first monitor for determining tool status, a second monitor for determining lot status and a processing unit for combining the tool status and the lot status to produce the status codes.
The processing unit produces the no operator code when the tool status is the tool idle code and the lot status is the waiting to be processed code. The processing unit also produces the idle no WIP code when the tool status is the idle tool code and there are no lots in queue to be processed. The system can include a network connecting the first monitor, the second monitor and the processing unit.
By distinguishing between different idle situations the invention is able to distinguish the magnitude of these idle situations which can, therefore, be understood and tracked which allows corrective action to be taken to reduce the impact of such idle situations. Further, the invention determines operator unavailability without monitoring the operator; as well as the amount of idle no WIP which is necessary to achieve reduced cycle time.